1. Field of the Invention
The present invention relates generally to repair of bone defects and more particularly, to systems, apparatus and methods of assisting growth of bone and tissue after trauma and surgery.
2. Description of Related Art
Regeneration of bone defects remains a significant clinical problem. For example, in oral reconstructive surgery, bone defects may occur as a result of tooth extraction, cyst formation, surgery, trauma, or destruction by periodontal or peri-implant disease. Some synthetic membrane materials have been used for guided tissue regeneration, including cellulose acetate filter, perforated Teflon®, mantle leaf, expanded polytetrafluoroethylene (PTFE), and resorbable polymers. Naturally derived membranes such as bovine collagen and lyophilized dura mater have also been used.
Membrane-assisted guided tissue regeneration techniques are based on the hypothesis that during wound healing, cells adjacent to the bone defect migrate to repopulate the defect at various rates. By placing a barrier such as a biocompatible membrane over the defect, the rapidly migrating connective tissue cells will be mechanically prevented from entering the defect. Theoretically, this allows the slower-migrating mesenchymal cells from the surrounding bone and marrow, having osteogenic potential, to repopulate the defect selectively.
A common feature of earlier synthetic membrane systems is macroporosity, which was believed to enhance regeneration by improving wound stability through tissue integration and allowing diffusion of extra-cellular nutrients across the membrane. However, in some applications, the use of macroporous biomaterials in the oral cavity can result in early bacterial contamination of the material. Bacterial contamination of macroporous biomaterials can result in antibiotic-resistant infection, which can require early removal of the device.
Additionally, a common feature of macroporous biomaterials is the ingrowth of surrounding tissues, which was thought to be necessary for stabilization of the implant. In macroporous biomaterials, cells readily incorporate into the material and connective tissue is manufactured. While this incorporation into the material slows the migration of cells, it presents a difficult problem to the patient and the surgeon during the removal process. The incorporated cells and fibrous connective material may make removal of the barrier painful and traumatic to the patient and very time consuming and difficult for the surgeon.
It has been discovered that the use of a flexible high-density polytetrafluoroethylene (PTFE) sheet material is useful in guided tissue regeneration. High density PTFE is substantially nonporous or microporous so as not to incorporate cells or attach to fibrous adhesions. By presenting a smooth surface to the biological materials, a high density PTFE barrier is easily inserted and removed following extended implantation periods. An example of a high density PTFE barrier material is disclosed in U.S. Pat. No. 5,480,711.
While high density PTFE medical barriers provide advantages over macroporous barriers, the smooth surface of the high density PTFE barriers sometimes leads to dehiscence of the soft tissue overlying the barrier. The dehiscence problem is caused by the fact that the smooth surface of high density PTFE will not incorporate cells and will not attach to fibrous adhesions. Thus, over the course of healing, the incision will occasionally split open over the high density PTFE barrier.